非线性超声技术检测P92耐热钢蠕变试验研究

Study on creep test of P92 heat resistant steel by nonlinear ultrasonic technology

深度调峰工况导致大容量高参数火电机组关键部件耐热钢材料性能劣化加速。作为一种大量用于火电机组的新型高温材料,P92钢的老化状态评估对于机组安全稳定运行具有重要意义。非线性超声信号能够填补传统无损检测方法在微尺度检测领域的空白,在材料早期损伤检测方面具有极大的应用潜力。利用非线性超声信号对微纳米尺度的微小缺陷和微裂纹比较敏感的特点,研究了P92钢耐热钢高温蠕变条件下微观组织形貌、析出相形态和成分的变化情况,试验得到P92钢蠕变时间与超声非线性系数之间的关系曲线,并根据材料的显微组织演变特征进行分析非线性超声系数的变化规律。试验表明,随着蠕变时间的增加,马氏体板条不断碎化,向等轴晶粒转变,碳化物不断沿晶界析出,少量在晶内析出,P92钢析出相颗粒平均尺寸在1000 h左右达到极大值490 mm后有所减小,析出相面积分数在2000 h左右增加到最大值0.089%后趋于稳定,析出相成分主要为块状的Cr23C6和碳化物;P92钢的二阶超声非线性系数随蠕变老化时间的变化曲线的拟合优度为0.94,比一阶超声非线性系数对蠕变老化更为敏感,并且与蠕变时间成正比关系,变化趋势与蠕变曲线类似。结果证明,非线性超声对于P92钢蠕变老化状态评估的可行性,为高温工况下P92钢非线性超声检测提供了理论依据。

The deep peak shaving condition leads to the accelerated deterioration of the properties of heat-resistant steel materials,which are the key components of large capacity and high parameter thermal power units.As was widely used in coal-fired power unit,the evaluation of P92 steel aging status is of great significance for the safe and stable operation of the power station.The nonlinear ultrasonic signal can fill the blank of traditional non-destructive testing methods in the field of micro-scale detection,which has great application potential in early damage detection of materials.In this work,the changes of micro-structure morphology,precipitated phase morphology and composition of P92 heat-resistant steel under high-temperature creep were studied by that the nonlinear ultrasonic signal is sensitive to micro defects and micro cracks at the micro-nano scale.And the relationship between creep time and ultrasonic nonlinear coefficient of P92 steel was obtained through experiments.The Variability of nonlinear ultrasonic coefficient was analyzed according to the evolution characteristics of microstructure of the material.The results showed that with the increase of creep time,the martensite laths are continuously crushed and transformed into equiaxed grains,and carbides are continuously precipitated along the grain boundaries,with a small amount of precipitation in the grains.The average size of precipitated phase particles in P92steel decreases after reaching the maximum value of 490 mm at about 1000h.Its area fraction of precipitated phase increases to the maximum 0.089%at about 2000h and then tends to be stable.The precipitated phases mainly consist of massive Cr23C6and carbides.The goodness of fit of the second-order ultrasonic nonlinear coefficient of P92 steel versus creep aging time is 0.94,which was more sensitive to creep aging,and monotonically increases with the increase of creep time,and the change trend is similar to the creep curve.The test results prove the feasibility of nonlinear ultrasonic testing for evaluating the creep aging state of P92 steel,and provide a theoretical basis for nonlinear ultrasonic testing of P92 steel under high temperature conditions.